U.S. patent number 6,983,035 [Application Number 10/669,613] was granted by the patent office on 2006-01-03 for extended multi-spot computed tomography x-ray source.
This patent grant is currently assigned to GE Medical Systems Global Technology Company, LLC. Invention is credited to Wayne Frederick Block, John Scott Price, Mark Vermilyea.
United States Patent |
6,983,035 |
Price , et al. |
January 3, 2006 |
Extended multi-spot computed tomography x-ray source
Abstract
Systems and methods for obtaining multi-slice images having a
total thickness of up to about 160 mm or more in a single gantry
rotation in computed tomography or volume computed tomography are
described. One embodiment comprises an extended, multi-spot x-ray
source for computed tomography or volume computed tomography
imaging, comprising: an electron gun capable of producing a
plurality of electron beams, each electron beam focused at a
predetermined distance and aimed in a predetermined direction; and
a plurality of targets positioned to receive the electron beams and
generate x-rays in response thereto, each target comprising a
predetermined focal spot thereon, wherein each electron beam is
synchronized to strike, at an appropriate time, a predetermined
target comprising a predetermined focal spot thereon.
Inventors: |
Price; John Scott (Wauwatosa,
WI), Block; Wayne Frederick (Sussex, WI), Vermilyea;
Mark (Niskayuna, NY) |
Assignee: |
GE Medical Systems Global
Technology Company, LLC (Waukesha, WI)
|
Family
ID: |
34313731 |
Appl.
No.: |
10/669,613 |
Filed: |
September 24, 2003 |
Prior Publication Data
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|
|
Document
Identifier |
Publication Date |
|
US 20050063514 A1 |
Mar 24, 2005 |
|
Current U.S.
Class: |
378/124; 378/4;
378/144 |
Current CPC
Class: |
H01J
35/147 (20190501); H01J 35/153 (20190501); H01J
35/10 (20130101); H01J 2235/086 (20130101) |
Current International
Class: |
H01J
35/08 (20060101) |
Field of
Search: |
;378/124,125,137,4-20,143,144 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Church; Craig E.
Attorney, Agent or Firm: Dougherty Clements Bernard;
Christopher L. Vogel; Peter J.
Claims
What is claimed is:
1. An extended multi-spot x-ray source for computed tomography or
volume computed tomography imaging, comprising: an electron gun for
producing a plurality of electron beams, each electron beam focused
at a predetermined distance and aimed in a predetermined direction;
a plurality of targets positioned to receive the electron beams and
generate x-rays in response thereto, each target comprising a
predetermined focal spot thereon, and at least one target
configured to let electron beams pass therethrough and strike
another target at predetermined intervals; and means for
synchronizing each electron beam to strike, at a predetermined
time, a predetermined target comprising a predetermined focal spot
thereon wherein at least one target comprises a cut-out section
that allows electron beams to pass therethrough and strike another
target at predetermined intervals.
2. The x-ray source of claim 1, wherein each target comprises a
different focal spot thereon.
3. The x-ray source of claim 1, wherein each electron beam is
focused at a different distance.
4. The x-ray source of claim 1, wherein each electron beam is aimed
in a different direction.
5. The x-ray source of claim 1, wherein each electron beam strikes
a different target having the appropriate focal spot thereon.
6. The x-ray source of claim 1, wherein the plurality of targets
rotate about an axis of rotation.
7. The x-ray source of claim 1, wherein a single electron beam,
focused at a predetermined distance, strikes only one target,
comprising a matching predetermined focal spot thereon, at a
time.
8. The x-ray source of claim 1, wherein adjusting an accelerating
voltage placed on the electron gun accomplishes at least one of:
focusing at least one electron beam, and changing electron beam
properties.
9. The x-ray source of claim 1, wherein multi-slice images having a
total thickness of up to about 160 mm can be obtained in a single
gantry rotation.
10. The x-ray source of claim 1, further comprising: a sensing
device for identifying a rotational position of the targets.
11. The x-ray source of claim 10, wherein the sensing device
comprises: a magnetic material disposed on a rotor; and a magnetic
pick-up device disposed in close proximity to the magnetic
material; wherein, when the rotor spins around its axis of
rotation, the magnetic pick-up device obtains a voltage or current
signal as the magnetic material passes thereby, and then the
magnetic pick-up device transmits an appropriately treated and
amplified signal to the electron gun to do at least one of: change
electron beam focusing parameters, and make deflection
corrections.
12. The x-ray source of claim 1, wherein adjusting a focal bias
voltage placed on the electron gun accomplishes at least one of:
focusing at least one electron beam, and changing electron beam
properties.
13. A method for obtaining thick multi-slice images in a single
gantry rotation in computed tomography or volume computed
tomography, the method comprising: providing an electron gun for
producing a plurality of electron beams, each electron beam focused
at a predetermined distance and aimed in a predetermined direction;
providing a plurality of targets positioned to receive the electron
beams and generate x-rays in response thereto, each target
comprising a predetermined focal spot thereon, and at least one
target configured to let electron beams pass therethrough and
strike another target at predetermined intervals; and synchronizing
each electron beam to strike, at a predetermined time, a
predetermined target comprising a predetermined focal spot thereon
wherein at least one target comprises a cut-out section that allows
electron beams to pass therethrough and strike another target at
predetermined intervals.
14. The method of claim 13, further comprising: adjusting an
accelerating voltage placed on the electron gun to accomplish at
least one of: focusing at least one electron beam, and changing
electron beam properties.
15. The method of claim 13, wherein multi-slice images having a
total thickness of up to about 160 mm can be obtained in a single
gantry rotation.
16. The method of claim 13, wherein each target comprises a
different focal spot thereon.
17. The method of claim 13, wherein each electron beam is focused
at a different distance.
18. The method of claim 13, wherein each electron beam is aimed in
a different direction.
19. The method of claim 13, wherein each electron beam strikes a
different target having the appropriate focal spot thereon.
20. The method of claim 13, wherein the plurality of targets rotate
about an axis of rotation.
21. The method of claim 13, wherein a single electron beam, focused
at a predetermined distance, strikes only one target, comprising a
matching predetermined focal spot thereon, at a time.
22. The method of claim 13, further comprising: providing a sensing
device for identifying a rotational position of the targets.
23. The method of claim 22, wherein the sensing device comprises: a
magnetic material disposed on a rotor; and a magnetic pick-up
device disposed in close proximity to the magnetic material,
wherein, when the rotor spins around its axis of rotation, the
magnetic pick-up device obtains a voltage or current signal as the
magnetic material passes thereby, and then the magnetic pick-up
device transmits an appropriately treated and amplified signal to
the electron gun to do at least one of: change electron beam
focusing parameters, and make deflection corrections.
24. The method of claim 13, further comprising: adjusting a focal
bias voltage placed on the electron gun to accomplish at least one
of: focusing at least one electron beam, and changing electron beam
properties.
25. A computed tomography or volume computed tomography imaging
system, comprising: an extended multi-spot x-ray source for
computed tomography or volume computed tomography imaging,
comprising: an electron gun for producing a plurality of electron
beams, each electron beam focused at a predetermined distance and
aimed in a predetermined direction; and a plurality of targets
positioned to receive the electron beams and generate x-rays in
response thereto, each target comprising a predetermined focal spot
thereon, and at least one target configured to let electron beams
pass therethrough and strike another target at predetermined
intervals; means for synchronizing each electron beam to strike, at
a predetermined time, a predetermined target comprising a
predetermined focal spot thereon; and an x-ray detector, wherein
the x-ray source projects a multi-spot beam of x-rays towards the
x-ray detector, the x-ray detector detects the x-rays, and an image
is created therefrom wherein at least one target comprises a
cut-out section that allows electron beams to pass therethrough and
strike another target at predetermined intervals.
Description
FIELD OF THE INVENTION
The present invention relates generally to computed tomography (CT)
imaging and volume computed tomography (VCT) imaging. More
specifically, the present invention relates to multi-spot x-ray
sources for CT imaging. Even more specifically, the present
invention relates to a stand-alone, self-contained electron gun,
having electron beams focusable at different distances, which
impinge on multiple targets to generate near-linear multi-spot
x-rays for CT and VCT imaging.
BACKGROUND OF THE INVENTION
Computed tomography (CT), sometimes called computed axial
tomography (CAT) or CAT scan, and volume computed tomography (VCT),
use special x-ray equipment to obtain image data from different
angles around a person's body, and then use computer processing of
the data to create a two-dimensional cross-sectional image (i.e.,
slice) or three-dimensional image of the body tissues and organs
that were scanned. CT and VCT imaging are particularly useful
because they can show a combination of several different types of
tissue (i.e., heart, lungs, stomach, colon, kidneys, liver, bone,
blood vessels, muscles, etc.) with high spatial resolution and a
great deal of clarity and contrast. Radiologists can interpret CT
and VCT images to diagnose various injuries and illnesses, such as
cardiovascular disease, trauma, cancer, and musculoskeletal
disorders. CT and VCT images can also be used to aid in minimally
invasive surgeries, and to allow for accurate planning and
pinpointing of tumors for radiation treatment, among other
things.
CT and VCT imaging allow structures within a body to be identified
and delineated without superimposing other structures on the images
created thereby. In a typical conventional CT or VCT imaging
system, an x-ray source emits a fan-shaped x-ray beam that is
collimated to lie within an X-Y plane of a Cartesian coordinate
system, generally referred to as the "imaging plane." The x-ray
beam passes through a section of the object being imaged, typically
a patient. After passing through the object and being attenuated
thereby, the x-ray beam impinges upon an array of radiation
detector elements. The intensity of the attenuated x-ray beam
radiation that is received by each detector element varies since
different parts of the body absorb and attenuate the x-rays
differently. Each detector element in the array produces a separate
electrical signal that is a measurement of the x-ray beam's
attenuation at each detector element. The attenuation measurements
from all the detector elements are acquired separately, and are
then combined to produce an image transmission profile.
Currently, x-ray sources for CT and VCT are limited to fairly
narrow "slices" for each revolution of the gantry because of the
well-understood "cone-beam artifact" problem, in which the "edges"
of the cone-like x-ray beam that emerges from a point source cannot
produce enough attenuation data, thereby resulting in portions of
the imaged object not being imaged at all. It would be desirable,
particularly for VCT, to have an extended or "linear" x-ray source
to eliminate or minimize the cone-beam artifact problem. That would
make it possible to obtain CT or VCT scans that cover an entire
organ in a single scan or revolution of the gantry. For example,
while existing CT and VCT imaging systems and methods allow
multi-slice images, having a total thickness of about 10 40 mm, to
be obtained in a single gantry rotation, it would be desirable to
have CT and VCT imaging systems and methods that allowed
multi-slice images having a total thickness as thick as 80 160 mm
or thicker to be obtained in a single gantry rotation. However,
improved CT and VCT imaging systems and methods are needed in order
for thicker multi-slice images to be realized.
Since existing CT and VCT imaging systems and methods have many
drawbacks, it would be desirable to have improved CT and VCT
imaging systems and methods that lack such restrictions. This
invention provides a single, near-linear, multi-spot x-ray source
that utilizes multiple x-ray targets having varying focal spots
thereon so as to improve the imaging data around the edges of the
object being imaged, thereby allowing thicker multi-slice images to
be obtained than currently possible.
SUMMARY OF THE INVENTION
Accordingly, the above-identified shortcomings of existing CT and
VCT imaging systems and methods are overcome by embodiments of the
present invention, which relates to a single, near-linear,
multi-spot x-ray source comprising multiple targets that have
varying focal spots thereon. Embodiments of this invention allow
thicker multi-slice images (up to about 80 160 mm thick or thicker)
to be obtained with each gantry rotation than currently possible
with existing CT and VCT imaging systems.
Embodiments of this invention comprise systems and methods for
obtaining thick total volume slices (i.e., up to about 160 mm or
thicker) in a single gantry rotation in computed tomography or
volume computed tomography. Embodiments of this invention comprise
an extended, multi-spot x-ray source for computed tomography and/or
volume computed tomography imaging. This x-ray source comprises: an
electron gun capable of producing a plurality of electron beams,
each electron beam focused at a predetermined distance and aimed in
a predetermined direction; and a plurality of targets positioned to
receive the electron beams and generate x-rays in response thereto,
each target comprising a predetermined focal spot thereon, wherein
each electron beam is synchronized to strike, at an appropriate
time, a predetermined target comprising a predetermined focal spot
thereon.
The plurality of targets rotate about an axis of rotation. Each
target comprises a different focal spot thereon, each electron beam
is focused at a different distance, and each electron beam is aimed
in a different direction. Each electron beam also strikes a
different target having the appropriate focal spot thereon. A
single electron beam, focused at a predetermined distance, strikes
only one target, comprising a matching predetermined focal spot
thereon, at a time.
At least one target is designed to let electron beams pass
therethrough and strike another target at predetermined intervals.
At least one target may comprise a cut-out section that allows
electron beams to pass therethrough and strike another target at
predetermined intervals.
The x-ray source may comprise a sensing device for identifying a
rotational position of the targets. The sensing device may
comprise: a magnetic material disposed on a rotor; and a magnetic
pick-up device disposed in close proximity to the magnetic
material, wherein when the rotor spins around its axis of rotation,
the magnetic pick-up device obtains a voltage or current signal as
the magnetic material passes thereby, and then the magnetic pick-up
device transmits an appropriately treated and amplified signal to
the electron gun to change electron beam focusing parameters and/or
to make deflection corrections.
Adjusting a focal bias voltage or an accelerating voltage placed on
the electron gun focuses at least one electron beam, and/or changes
the electron beam properties. A total volume slice (i.e., a total
thickness of the multi-slice images) of up to about 80 mm to about
160 mm thick or thicker can be obtained in a single gantry
rotation.
Embodiments of this invention also comprise a computed tomography
or volume computed tomography imaging system. These systems
comprise an extended, multi-spot x-ray source. This x-ray source
comprises: an electron gun capable of producing a plurality of
electron beams, each electron beam focused at a predetermined
distance and aimed in a predetermined direction; and a plurality of
targets positioned to receive the electron beams and generate
x-rays in response thereto, each target comprising a predetermined
focal spot thereon, wherein each electron beam is synchronized to
strike, at an appropriate time, a predetermined target comprising a
predetermined focal spot thereon; and an x-ray detector, wherein
the x-ray source projects a multi-spot beam of x-rays towards the
x-ray detector, the x-ray detector detects the x-rays, and an image
is created therefrom.
Further features, aspects and advantages of the present invention
will be more readily apparent to those skilled in the art during
the course of the following description, wherein references are
made to the accompanying figures which illustrate some preferred
forms of the present invention, and wherein like characters of
reference designate like parts throughout the drawings.
DESCRIPTION OF THE DRAWINGS
The systems and methods of the present invention are described
herein below with reference to various figures, in which:
FIG. 1 is a schematic drawing showing one embodiment of a CT
imaging system that may be utilized in embodiments of this
invention;
FIG. 2 is a schematic drawing showing the architecture of the CT
imaging system shown in FIG. 1;
FIG. 3 is a schematic diagram showing an embodiment of a
self-contained electron gun that produces an electron beam that can
be sequentially focused at different distances, wherein the
electron beam sequentially strikes a different target having a
different focal spot thereon, which yields a near-linear multi-spot
x-ray source useful for CT and VCT imaging;
FIG. 4 is a schematic diagram showing multiple targets, some
notched, each having a different focal spot thereon, as utilized in
embodiments of this invention; and
FIG. 5 is a schematic diagram showing a sensing coil that produces
a rotation-angle-dependent signal, which is used to trigger changes
in electron beam focusing in the electron gun from one target to
the next, as utilized in embodiments of this invention.
DETAILED DESCRIPTION OF THE INVENTION
For the purposes of promoting an understanding of the invention,
reference will now be made to some preferred embodiments of the
present invention as illustrated in FIGS. 1 5 and specific language
used to describe the same. The terminology used herein is for the
purpose of description, not limitation. Specific structural and
functional details disclosed herein are not to be interpreted as
limiting, but merely as a basis for the claims as a representative
basis for teaching one skilled in the art to variously employ the
present invention. Any modifications or variations in the depicted
support structures and methods, and such further applications of
the principles of the invention as illustrated herein, as would
normally occur to one skilled in the art, are considered to be
within the spirit and scope of this invention.
This invention relates to systems and methods for minimizing or
eliminating the cone-beam artifact problem in CT images,
particularly VCT images, to allow thicker multi-slice images to be
obtained with each gantry rotation. Referring now to FIG. 1, there
is shown a schematic diagram showing an exemplary CT imaging system
10 that may be utilized in embodiments of this invention. Such
systems generally comprise a gantry 12, a gantry opening 48, and a
table 46 upon which a patient 22 may lie. Gantry 12 comprises an
x-ray source 14 that projects a beam of x-rays 16 toward an array
of detector elements 18. During operation, gantry 12 rotates about
a center of rotation 24 to obtain an image of one or more "slices"
of an area of interest in a patient 22. Generally, the array of
detector elements 18 comprises a plurality of individual detector
elements 20 that are arranged in a side-by-side manner in the form
of an arc that is essentially centered on x-ray source 14. In
multi-slice imaging systems, parallel rows of arrays of detector
elements 18 can be arranged so that each row of detectors can be
used to simultaneously generate multiple thin slice images through
patient 22 in the X-Y plane. Each detector element in the array of
detector elements 18 senses and detects the x-rays 16 that pass
through an object, such as patient 22, and then an image is created
therefrom. While this figure shows the x-ray source 14 and the
array of detector elements 18 aligned in the X-Y plane, some CT
imaging systems may align the x-ray source 14 and the array of
detector elements 22 differently, without deviating from the spirit
and scope of this invention.
Referring now to FIG. 2, there is shown a schematic diagram showing
the architecture of the CT imaging system shown in FIG. 1. The
rotation of gantry 12 and the operation of x-ray source 14 are
governed by a control mechanism 26 of CT imaging system 10. Control
mechanism 26 includes an x-ray controller 28 that provides power
and timing signals to x-ray source 14, and a gantry motor
controller 30 that controls the rotational speed and position of
gantry 12. A data acquisition system (DAS) 32 in control mechanism
26 samples analog data from the individual detector elements 20,
and converts that analog data to digital signals for subsequent
processing in accordance with the methods and systems of this
invention. An image reconstructor 34 receives the sampled and
digitized x-ray data from DAS 32 and performs high speed image
reconstruction thereon. The reconstructed image is then applied as
input to a computer 36, which can store the image in a mass storage
device 38. Computer 36 may also retrieve stored images from the
mass storage device 38 for later viewing.
Computer 36 may also receive commands and scanning parameters from
an operator via an operator console 40, which may comprise a
keyboard, touchpad, or other suitable input device. An associated
cathode ray tube display 42 (or other suitable display) may allow
the operator to view the reconstructed image and other data from
computer 36. The operator supplied commands and parameters may be
used by computer 36 to provide control signals and information to
DAS 32, x-ray controller 28 and gantry motor controller 30.
Additionally, computer 36 may operate a table motor controller 44
which can control a motorized table 46, thereby allowing the
patient 22 to be properly positioned within gantry 12 or moved
therethrough. For example, table 46 may move portions of patient 22
through gantry opening 48 in the Z-direction.
Embodiments of the present invention may make use of software or
firmware running on computer 36. A mouse or pointing device may be
employed to facilitate the entry of data and/or image locations.
Other embodiments of this invention may utilize a general purpose
computer or workstation having a memory and/or printing capability
for storing or printing images. Suitable memory devices are well
known and include, but are not limited to, RAM, diskettes, hard
drives and optical media. Embodiments using such stand-alone
computers or workstations may receive data from CT imaging system
10 via conventional electronic storage media or via a conventional
communications link, and images may then be reconstructed
therefrom.
Generally, x-ray sources for CT and VCT comprise single focal spot
x-ray tubes 14 mounted on gantry 12. Such x-ray sources produce a
single fan-like x-ray beam that is aimed at the array of detector
elements 18. However, there are drawbacks for such single focal
spot x-ray sources: (1) such x-ray sources limit the image that can
be obtained to fairly narrow "slices" per each gantry revolution
(i.e., slices having a total combined thickness of about 10 40 mm);
and (2) such sources also lead to the cone-beam artifact problem,
in which there is not enough data to be detected on the "edges" of
the cone-like beam emerging from such point sources. Therefore, in
order to increase the z-axis coverage, an extended x-ray source is
needed to produce a linear or near-linear x-ray source effect so
that sufficient information for large organ scans can be gathered
with a single gantry revolution. While using multiple x-ray sources
arranged in a linear fashion is one possible solution, it is a very
expensive and cumbersome solution to the problem, and is therefore
not very practical. This invention, on the other hand, provides a
much less expensive and less cumbersome solution to the problem,
making it ideal for extending the x-ray source in the z-direction.
Additionally, this invention allows multi-slice images as large as
80 160 mm thick, or sometimes even thicker, to be obtained in a
single gantry rotation.
Referring now to FIG. 3, there is shown a schematic diagram showing
an embodiment of this invention comprising a single self-contained
electron gun 50 that produces an electron beam 52 that can be
sequentially focused at different distances, wherein the electron
beam 52 sequentially strikes a different target 62A, 62B, 62C
having a different focal spot thereon. While there are three
targets 62A, 62B, 62C shown in this embodiment, this is in no way
meant to be limiting on this invention. In fact, other embodiments
of this invention may comprise other numbers of targets, such as
anywhere from 2 6 different targets 62, with each target 62 having
a different focal spot thereon. Also, depending on the application,
even more than 6 targets could be used, if desired.
This invention comprises a single, self-contained electron gun 50
that produces focused electron beams 52 independent of most tube
geometry features. This electron gun 50 may comprise a General
Electric Imatron electron gun. As shown in FIG. 3, the electron gun
50 comprises an electron source 54, apertures 56, accelerating
and/or focusing electrodes 58, and steering electrodes 60. This
electron gun 50 produces focused electron beams 52, each having a
different focal length and direction. The electron beams 52
produced hereby can be focused, and the electron beam properties
can be changed rapidly, by adjusting the focal bias voltages placed
on parts inside the electron gun 50. By focusing in this manner,
the electron gun 50 is free from the focusing effect of the tube
geometry, and can therefore be controlled by simply changing the
accelerating and bias voltages within the electron gun 50
structure. In embodiments, the electron gun 50 may be aimed at a
stack of slotted targets 62 that are mounted on a straddle support
64 for ideal gantry movement load distribution. The targets 62 may
comprise molybdenum (Mo), and the targets 62 may be mounted on a
shaft 66 comprising tungsten (W) alloyed with about 5 10% rhenium
(Re). The targets 62 and shaft 66 may also comprise any other
suitable materials. The electron gun 50 may be isolated from nearby
objects at ground potential with high-density alumina or other
insulation material suitable for high voltage electrostatic
isolation.
In embodiments, the electron gun 50 may be aimed roughly parallel
to the axis of rotation 65 of a stacked ensemble of multiple
targets 62 that form an anode having several different focal spots.
X-rays 16 may emerge from the targets 62 at a proper range of
angles between the cut-off due to the heel effect, and that angle
plus the usable angle imposed by cone-beam artifacts and
reconstruction limits. Several targets 62A, 62B, 62C may be mounted
on shaft 66, which is mounted on a straddle support 64. The
straddle support 64 may comprise one or more sets of ball bearing
assemblies, and ideally, distributes the mechanical load over the
ball bearing assemblies to improve the bearing operation and yield
longer bearing life. The shaft 66, on which the targets are stacked
and mounted, may comprise a hollow channel 67 therein so that
liquid coolant, water or other suitable substance 68 can circulate
freely therein to cool the targets 62A, 62B, 62C. Since the targets
62A, 62B, 62C and anode structure are at ground potential, cooling
fluid 68 may be supplied thereto via pumps and hoses/lines. This
grounded target design is a simplified high efficiency motor (HEM)
design, since a close distance between the rotor (enclosed in a
vacuum vessel) and the stator (in atmosphere or in oil or other
cooling fluid) provides close magnetic coupling between the two
motor elements.
Referring now to FIG. 4, there is shown a schematic diagram showing
multiple targets 62A, 62B, 62C, some notched, each having a
different focal spot thereon, as utilized in embodiments of this
invention. As shown herein, the first target 62A comprises large
notches 80, while the second target 62B comprises small notches 82,
and the third target 62C is not notched at all. The large notches
80 in the first target 62A allow the electron beam 52 to pass
through the first target 62A and either strike or pass through the
second target 62B, as appropriate, while the small notches 82 in
the second target 62B allow the electron beam 52 to pass through
the second target 62B and strike the third target 62C. In
embodiments, the third target 62C comprises a focal spot 83C
thereon from about 0 40.degree., the second target 62B comprises a
focal spot 83B thereon from about 40 80.degree., and the first
target 62A comprises a focal spot 83A thereon from about 80
120.degree.. The large notches 80 in the first target 62A are shown
here in this embodiment as comprising cut-out sections from about 0
80.degree., 120 200.degree., and 240 320.degree., while the small
notches 82 in the second target 62B are shown here as comprising
cut-out sections from about 0 40.degree., 120 160.degree., and 240
280.degree.. While the notches 80, 82 herein are shown as
pie-shaped cut-outs, various other cut-outs are possible without
deviating from the spirit and scope of this invention. For example,
the notches could comprise windows cut-out from around the
periphery of the targets 62, or could comprise any other suitable
shape or design that allows the electron beam 52 to pass through
the target 62 and strike or pass through the next target 62.
Additionally, while each target 62A, 62B herein is shown having
three notches therein 80, 82 respectively, numerous other
cut-out/notching arrangements are possible within the scope of this
invention.
The electron gun 50 is designed to allow the focal spot of the
electron beam 52 that is being emitted at a specific time to be
synchronized with the target 62 comprising that particular focal
spot thereon. For example, while the targets 62A, 62B, 62C are
rotating with shaft 66, there are predetermined times when the
third target 62C is to be struck by the electron beam 52 (and
accordingly, the electron beam 52 passes through the first target
62A and the second target 62B at that time), then when the second
target 62B is to be struck by the electron beam 52 (and
accordingly, the electron beam 52 passes through the first target
62A at that time), and then when the first target 62A is to be
struck by the electron beam 52. Since all three targets 62A, 62B,
62C have different focal spots 83 thereon, the electron beam focus
is controlled so that the electron gun 50 emits an electron beam 52
having the appropriate focal length for the given target it is to
strike at that time.
In embodiments of this invention, the electron gun 50 is controlled
by obtaining a signal from a magnetic pick-up device such as the
one shown in FIG. 5, which functions as an odometer or tachometer
and produces a rotational phase-determined signal. As shown herein
in this non-limiting embodiment, a sensing device for identifying
the rotational position of the targets comprises a slug or pin of
magnetic material 90 embedded in the rotor 92, and a magnetic
pick-up device 94 disposed in close proximity thereto. As the rotor
92 spins around its axis of rotation 95, the magnetic pick-up
device 94 (shown here as being a B-flux sensing coil), obtains a
voltage or current signal each time the magnetic slug 90 passes the
sensing coil 94. An appropriately treated and amplified signal can
then be transmitted to the electron gun 50 to change the electron
beam focusing parameters and, if necessary, to make any deflection
corrections that may be needed to optimize the performance of this
multi-spot x-ray source. In this manner, an entire revolution of
the rotor 92 can be accounted for, and the focal length of the
electron beam 52 can be adjusted and controlled so that the
electron gun 50 emits an electron beam 52 having the appropriate
focal length, depending upon which target 62A, 62B, 62C the
electron beam 52 is supposed to strike at a particular time.
For example, initially, and while the rotating target assembly has
an angular orientation of about 0 40.degree., the electron gun 50
may emit an electron beam 52 that strikes the third target 62C.
Then, after a predetermined period of time, and while the rotating
target assembly has an angular orientation of about 40 80.degree.,
the electron gun focusing parameters could change and cause the
electron gun 50 to emit an electron beam 52 that strikes the second
target 62B. Then, after another predetermined period of time, and
while the rotating target assembly has an angular orientation of
about 80 120.degree., the electron gun focusing parameters could
change again and cause the electron gun 50 to emit an electron beam
52 that strikes the first target 62A. This can continue in
40.degree. increments until the rotor 92 has made one complete
revolution, after which the cycle may start over again from the
beginning, with the electron gun 50 emitting an electron beam 52
that strikes the third target 62C, then the second target 62B, then
the first target 62A, etc. While 40.degree. increments have been
described herein, this is in no way meant to be limiting on this
invention as other angular increments could clearly be used
too.
The bias voltages of the electron gun 50 that determine the focal
length of the electron beam may be established in 10's of
.mu.seconds. This is fast enough to accomplish the necessary
switching of the focusing parameters since the targets 62A, 62B,
62C rotate at about 120 Hz or 8.0 msec/revolution, which is
approximately 20 .mu.sec/degree. The electron guns 50 of this
invention may allow the electron beam source to be handled as a
complete sub-assembly, thereby making it easier to replace, align,
design and improve the electron beam source independent of the
remaining x-ray tube insert geometry.
As described above, this invention provides an extended,
near-linear multi-spot x-ray source that allows thicker multi-slice
images to be obtained than currently possible with existing CT
and/or VCT imaging systems. Advantageously, this invention utilizes
a combination of known target and x-ray source technology to yield
a near-linear x-ray source, which can ideally be utilized in CT
and/or VCT imaging systems. This invention comprises a single
self-contained electron gun that produces focused electron beams
that are independent of most tube geometry features. These electron
beams have different focal lengths, with each beam being designed
to strike a different target, which creates a near-linear,
multi-spot x-ray source. The targets are designed to allow the
electron beams to pass therethrough when required, so that more
distant targets can be struck by the electron beam. The multiple
targets in this invention allow multi-spot x-rays to be generated
from a single source, and the multi-spot x-ray source of this
invention allows a number of previously inaccessible diagnostic
techniques to be realized, of which whole organ scanning in a
single CT or VCT scan is only one. Many other advantages will also
be apparent to those skilled in the relevant art.
Various embodiments of this invention have been described in
fulfillment of the various needs that the invention meets. It
should be recognized that these embodiments are merely illustrative
of the principles of various embodiments of the present invention.
Numerous modifications and adaptations thereof will be apparent to
those skilled in the art without departing from the spirit and
scope of the present invention. For example, while the embodiments
shown and described herein utilized three targets, it will be
appreciated by those skilled in the art that this invention may
comprise other numbers of targets without deviating from the spirit
and scope of this invention, and all such variations are intended
to be covered herein. Additionally, while pie-shaped cut-out
notches were described herein as a means of letting the electron
beams pass through a particular target, numerous other designs are
possible, and are also intended to be covered herein. Thus, it is
intended that the present invention cover all suitable
modifications and variations as come within the scope of the
appended claims and their equivalents.
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